1. Field
This application relates to arrangements for the solid state ion-conducting electrolyte elements in an ion- conducting device, and more particularly to modular arrangements for multi-element ion-conducting devices.
2. State of the Art
Solid state ion-conducting electrolyte elements are typically constructed from materials capable of conducting, or permitting passage of, specific ions through the element. Various electrolyte materials will allow specific ions of a certain size or type to pass through the element from one side to the other. Materials having this capability include ceramic metal oxides such as bismuth oxide and cerium oxide, polymeric electrolyte membranes, and immobilized molten electrolyte membranes. The membranes are more pliant than the metal oxides, but conduct ions in a similar manner. Zeolyte membranes having pore sizes allowing diffusion of certain sized molecules across the membrane are also used for specific ion conduction. Each type of metal oxide or membrane electrolyte finds use in a different ion-conducting application.
The electrolyte elements, especially the ceramic metal oxides, are often formed as flat plates having an electrically conductive material attached to one or both of the plate's flat surfaces. When the electrode material comes in contact with a gas containing the uncharged form of the ionic species, an electrochemical reaction occurs at the electrode to produce the specific ion. The liberated ion may then migrate through the electrolyte element.
Ion-conducting devices typically utilize a plurality of electrolyte elements arranged whereby each element is spaced apart from successive elements. The spaces allow reactant gases necessary for ion-conducting activity to flow between the electrolyte elements, and come in contact with the electrode material attached to the surface of each element.
Ion-conducting devices find use in a variety of applications including fuel cells, steam electrolyzers, oxygen concentrators, and other types of electrochemical reactors. When used in fuel cell applications, fuel gases such as H.sub.2, CH.sub.4 containing gases, synfuels, or light hydrocarbon fuel stocks, are directed to one face of the spaced-apart elements, and air is directed to the opposing face. When used as an oxygen concentrator, air is directed to one face of the elements, and pure molecular oxygen is collected from the opposite face. Other ion-conducting devices function in a similar manner, but may have structural modifications, and different reactant gas requirements.
As previously stated, reactant gases flowing between the spaced-apart electrolyte elements come in contact with, and react at, the electrode material attached to the surface of the elements. For example, at one electrode surface of a fuel cell, an electrochemical reaction occurs in which an ionic species, such as O.sup.-2 from air, is produced and conducted across the thickness of the element to the other electrode surface where it reacts with the fuel gas to form water and CO.sub.2. In a typical fuel cell, this electrochemical reaction may be illustrated by the following equations: